github/jooq
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

[#1502] Document implicit JOIN

Browse Source
This commit is contained in:
lukaseder 2018-02-12 10:33:30 +01:00
parent 3546388af1
commit 72f7b3d7d1
1 changed files with 111 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

111
jOOQ-manual/src/main/resources/org/jooq/web/manual-3.11.xml
View File

@ -4827,6 +4827,117 @@ WHERE NOT EXISTS (
</html></content>
</section>
<section id="implicit-join">
<title>Implicit JOIN</title>
<content><html>
<p>
In SQL, a lot of <reference id="join-clause" title="explicit JOIN clauses"/> are written simply to retrieve a parent table's column from a given child table. For example, we'll write:
</p>
</html><sql><![CDATA[-- Get all books, their authors, and their respective language
SELECT
a.first_name,
a.last_name,
b.title,
l.cd AS language
FROM book b
JOIN author a ON b.author_id = a.id
JOIN language l ON b.language_id = l.id;
-- Count the number of books by author and language
SELECT
a.first_name,
a.last_name,
l.cd AS language,
COUNT(*)
FROM book
JOIN author a ON b.author_id = a.id
JOIN language l ON b.language_id = l.id
GROUP BY a.id, a.first_name, a.last_name, l.cd
ORDER BY a.first_name, a.last_name, l.cd]]></sql><html>
<p>
There is quite a bit of syntactic ceremony (or we could even call it "noise") to get a relatively simple job done. A much simpler notation would be using implicit joins:
</p>
</html><sql><![CDATA[-- Get all books, their authors, and their respective language
SELECT
b.author.first_name,
b.author.last_name,
b.title,
b.language.cd AS language
FROM book b;
-- Count the number of books by author and language
SELECT
b.author.first_name,
b.author.last_name,
b.language.cd AS language,
COUNT(*)
FROM book
GROUP BY
b.author_id,
b.author.first_name,
b.author.last_name,
b.language.cd
ORDER BY
b.author.first_name,
b.author.last_name,
b.language.cd]]></sql><html>
<p>
Notice how this alternative notation (depending on your taste) may look more tidy and straightforward, as the semantics of accessing a table's parent table (or an entity's parent entity) is straightforward.
</p>
<p>
From jOOQ 3.11 onwards, this syntax is supported for to-one relationship navigation. The code generator produces relevant navigation methods on generated tables, which can be used in a type safe way. The navigation method names are:
</p>
<ul>
<li>The parent table name, if there is only one foreign key between child table and parent table</li>
<li>The foreign key name, if there are more than one foreign keys between child table and parent table</li>
</ul>
<p>
This default behaviour can be overridden by using a <reference id="codegen-generatorstrategy" title="Code Generator Strategy"/>.
</p>
<p>
The jOOQ version of the previous queries looks like this:
</p>
</html><java><![CDATA[// Get all books, their authors, and their respective language
create.select(
BOOK.author().FIRST_NAME,
BOOK.author().LAST_NAME,
BOOK.TITLE,
BOOK.language().CD.as("language"))
.from(BOOK)
.fetch();
// Count the number of books by author and language
create.select(
BOOK.author().FIRST_NAME,
BOOK.author().LAST_NAME,
BOOK.language().CD.as("language"),
count())
.from(BOOK)
.groupBy(
BOOK.AUTHOR_ID,
BOOK.author().FIRST_NAME,
BOOK.author().LAST_NAME,
BOOK.language().CD)
.orderBy(
BOOK.author().FIRST_NAME,
BOOK.author().LAST_NAME,
BOOK.language().CD)
.fetch();]]></java><html>
<p>
The generated SQL is almost identical to the original one - there is no performance penalty to this syntax.
</p>
</html></content>
</section>
<section id="where-clause">
<title>The WHERE clause</title>
<content><html>